The present invention relates to screen printing machines in general, and more particularly to improvements in means for mounting a squeegee in the interior of the moving stencil or screen of a screen printing machine.
It is already known to utilize in a screen printing machine a squeegee which resembles an elongated doctor blade and is secured to a holder which, in turn, is movably mounted on a support. A gas-filled deformable cushion is interposed between the support and the holder to bias the squeegee against the internal surface of the stencil. Such screen printing machines exhibit the drawback that the entire weight of the squeegee, plus the weight of the holder, rests on the internal surface of the stencil, and that the pressure due to such combined weight is augmented by the bias of the cushion which urges the squeegee against the internal surface of the stencil. If the squeegee is a blade, the edge portion of the blade is urged against the stencil with a very large force which can be readily withstood only if the blade consists of a high-grade steel or the like. The material of the blade is stressed not only due to the aforementioned bias of the cushion augmented by the weight of the blade and its holder, but also by the moving stencil which tends to flex the edge portion of the blade sideways. Still further, the blade must be sufficiently resistant to avoid undesirable oscillation in response to shaking and/or other stresses. Consequently, the blade is normally a relatively thick, sturdy and heavy piece of steel. However, even such sturdy blades are incapable of invariably standing all stresses which arise in the operation of a screen printing machine, for example, in response to changes in the speed of the stencil. It has been found that changes in the speed of the stencil cause a shift in the locus where the edge portion of the blade engages the internal surface of the stencil, and this can affect the quality and reproducibility of the printing operation.